Thermosetting resins such as phenol resins, melamine resins, epoxy resins, unsaturated polyester resins, and bismaleimide resins are based on thermosetting properties and are excellent in water resistance, chemical resistance, heat resistance, mechanical strength, and reliability. Accordingly, thermosetting resins have been widely used in various industrial fields.
However, the phenol resins and the melamine resins have drawbacks in that volatile byproducts are generated during hardening, the epoxy resins and the unsaturated polyester resins have a drawback of poor flame retardancy, and the bismaleimide resins have a drawback of very high costs.
In order to solve the drawbacks, there has been studied polybenzoxazime obtained by performing a ring-opening polymerization reaction on a benzoxazine ring, which leads to thermosetting, without the generation of volatile matter, which is considered to be a problem.
To obtain a thermosetting resin having a benzoxazine ring in the molecular structure thereof, an oxazine ring is opened by heating and polymerization is performed without the generation of byproducts. Accordingly, the thermosetting resin having the benzoxazine ring is receiving attention as a thermosetting resin used in an encapsulant, an impregnating agent, a laminate, an adhesive, a paint, a coating material, a friction material, FRP, and a molding material. The benzoxazine ring has a complex structure including benzene and oxazine rings.
Polybenzoxazines are hardened polymers having a high glass transition temperature (Tg), low permittivity, high tension, a low coefficient of thermal expansion, excellent elasticity, and low hygroscopicity, thus maintaining a balance between mechanical, electrical, and chemical properties.
Techniques for further enhancing the properties of polybenzoxazines have been continuously developed. For example, Korean Laid-Open Patent Application No. 10-2012-0058566 relates to a “polybenzoxazime composition”, and discloses a method of preparing polybenzoxazime having favorable thermal stability, the method including heating a curable composition including a benzoxazine compound and a pentafluoroantimony acid catalyst at a sufficient temperature for a sufficient time to thus achieve polymerization.
Further, Korean Patent No. 10-0818254 relates to “a polybenzoxazime-based compound, an electrolyte membrane including the same, and a fuel cell using the same”, and discloses a novel polybenzoxazime-based compound having improved acid trapping performance, mechanical and chemical stability, and ability to retain phosphoric acid at high temperatures, an electrolyte membrane using the same, and a method of preparing the same.
With recently increased interest in the environment at home and abroad, environmental problems have started to become an issue in the electronic material industry. Due to the RoHS directive, which limits the use of hazardous substances in the European Union and developed countries, eco-friendly lead-free PCB technologies are increasingly adopted in the domestic electronic circuit board industry. As lead is not used during an eco-friendly lead-free process, the working temperature is increased during the process. Accordingly, materials that can withstand high temperatures and equipment suitable for the materials must be developed.
Epoxy resins are frequently used as coatings, insulation, building materials, and adhesives, where they help ensure easy handling, high stability, and excellent mechanical and chemical properties. An epoxy resin composition needs to have heat resistance and flame retardancy for the purpose of lead-free application. Particularly, in the case of a CCLS (copper clad laminate sheet) epoxy resin composition, the V-0 certification of the UL-94 standard is essentially required. In the related art, a halogenated resin, such as a brominated epoxy resin, and antimony oxide are used to impart the flame retardancy.
Current halogen-based flame retardants generate gas during injection and dioxin during incineration, thus negatively affecting the environment. The electric, electronic, and semiconductor industries are major industries in Korea, and account for a large portion of industry in Korea. Particularly, there is a great demand for a semiconductor-industry technique regarding the flame retardancy of the encapsulant and the adhesive for semiconductors, and there is growing interest in the development of a raw material for replacing the flame retardant, which is harmful to the environment.
As an alternative thereof, the use of polybenzoxazime, which is a phenol-based hardening agent, has been emphasized. As described above, polybenzoxazime is a thermosetting polymer obtained by polymerizing a benzoxazine-based monomer while a ring is opened in a molecule of the monomer by heat. Polybenzoxazime can be self-hardened without byproducts and does not generate volatile materials and is not changed in volume while hardening, thus ensuring excellent dimensional stability. Further, polybenzoxazime is a highly heat-resistant polymer having a high glass transition temperature and decomposition of less than 1% at thermal decomposition temperatures up to 350° C. Further, since polybenzoxazime is a nitrogen-containing compound suitable for use in halogen-free products, it serves as a flame retardant.
However, conventionally developed polybenzoxazime fails to exhibit a sufficient flame-retardant effect, and accordingly, additives such as bromine, phosphorus, or chlorine compounds are added to the polybenzoxazime-containing flame retardant. These additives are not dissolved in a solvent and thus result in a hardened resin that may cause problems during a processing process and that has poor oxidative stability at high temperatures and poor physical properties.
Therefore, there is a need to prepare highly flame-retardant polybenzoxazime that may be used in high-temperature environments without revealing the above-described drawbacks.
Meanwhile, a copper clad laminate (CCL) is a laminate with a thin copper foil on an insulating material. In accordance with the recent high performance and high integration of smart devices, a copper clad laminate used in a printed circuit board (PCB) is required to have excellent heat resistance and low permittivity. A resin is used as the base material of the copper clad laminate, and serves as an insulator in the printed circuit board. Permittivity must be low in order to form an excellent insulator. “Permittivity” refers to the degree of polarization of molecules in a nonconductor relative to an external electrical signal. The smaller the permittivity, the better the insulating performance. As the permittivity of the insulator is reduced during the operation of the printed circuit board, the processing speed of the signal is increased and a transmission loss is reduced.
As an alternative to satisfy the requirements for heat resistance and low permittivity of the above-described copper clad laminate, the use of polybenzoxazime, which is a phenol-based hardening agent, has been emphasized. As described above, polybenzoxazime is a thermosetting polymer obtained by polymerizing a benzoxazine-based monomer while a ring is opened in a molecule of the monomer by heat. Polybenzoxazime can be self-hardened without byproducts, does not generate volatile materials, and is not changed in terms of volume during hardening, thus ensuring excellent dimensional stability.
(Patent Document 1) Korean Laid-Open Patent Application No. 10-2012-0058566
(Patent Document 2) Korean Patent No. 10-0818254